The arrangement of repetitious human DNA sequences, their possible interspersion with unique DNA, and the relationship of these sequences to transcription products will be examined by a very simple direct procedure. The structures in long DNA fragments isolated on the basis of their rapid renaturation rate will be determined by electron microscopy under conditions in which double and single strands can be visualized. The same structures after shearing will then be classified by renaturation kinetics under standard conditions. From these renaturation studies coupled with the observed structures, it is possible to determine the detailed arrangement of repeats. Subsequent to this study, long RNA transcripts would be examined by an analogous procedure, repetitive sequences in RNA being isolated as hybrids by renaturation with long DNA fragments. Structural and kinetic assignments would then be made by the above approach. Highly repetitive sequences will also be examined by microscopy as a control to the above proposal. If nonhomologies are observed in heteroduplexes of these sequences, this would imply an interspersion of repeat elements. Satellite sequences, isolated from a density gradient, would then be examined for this interspersion with the goal of comparing the arrangement of repeat elements in specific satellite sequences with the arrangement occurring in total highly repetitious DNA isolated from whole DNA by renaturation kinetics.